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archimedes
Silver Member
United Kingdom
191 Posts |
 Posted - 06/29/2009 : 11:18:27
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Hi folks
Still tuning my OD-3 and after a lot of experimentation and am a lot closer - very, very close in fact to what I am after. With the values below I have got a thick, tight, warm sound with no fizziness, very British amp like. I did try some different diode options but headed back to stock for those. It's mostly tone I have been working with.
C22 .01 - tried higher values here but didn't like the change in the effect
C23 .1
C16 .022
Running a NE5532 op amp and C13 at .047 from a previous mod
There is a lot of low end now which I like but ideally I would like a way to roll off some of the bass with a trimpot. Can anyone point me in the right direction? R24 maybe? Any suggestions would be most helpful.
Thanks
David |
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cctsim
Silver Member
United Kingdom
418 Posts |
Posted - 06/29/2009 : 20:26:27
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I don't like trimpots personally.
To roll off the bass, I would try to change C13 to either 0.010uF or 0.022uF.
Same with C15, try 0.047uF or smaller.
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archimedes
Silver Member
United Kingdom
191 Posts |
Posted - 06/29/2009 : 21:25:07
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quote:
Originally posted by cctsim
I don't like trimpots personally.
To roll off the bass, I would try to change C13 to either 0.010uF or 0.022uF.
Same with C15, try 0.047uF or smaller.
Many thanks for those suggestions.
I have just been trying it for recording, normally I use the Tiny Terror direct but I wanted to see how the mods stand up. Pretty good I think although as I said maybe just a tad too much low end, not much though and that beefiness is what makes it sound more natural to my ears.
David |
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cctsim
Silver Member
United Kingdom
418 Posts |
Posted - 06/29/2009 : 22:19:04
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I run a few simulations of the OD3 tone circuit and it seems a trimpot at R24 will not have the desired effect. Changing R24 shifts the frequency response down but keeps the shape the same. This graph is for R24 = 1k (green curve), 2k (blue curve) and 5k (red curve). I believe this will only reduce the output with no change in bass perception.
I found it is far more effective to change C14. This graph is for C14= 10u, 1u, 0.47u and 0.1u. The green curve is the original. I can see now your complaints about too much bass.
My previous suggestion to lower C13 seems not to affect the lower frequencies but it amplifies the higher frequencies like a treble booster.
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archimedes
Silver Member
United Kingdom
191 Posts |
Posted - 06/30/2009 : 00:09:28
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quote:
Originally posted by cctsim
I found it is far more effective to change C14. This graph is for C14= 10u, 1u, 0.47u and 0.1u. The green curve is the original. I can see now your complaints about too much bass.
Wow! Thank you so much for all your efforts. It will be a few days until I get to try this but I'll let you know how I get on.
David |
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 06/30/2009 : 03:06:33
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| cctsim strikes again... that's awesome mate! |
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cctsim
Silver Member
United Kingdom
418 Posts |
Posted - 06/30/2009 : 13:22:11
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| Cheers Guys, PM if anyone wants the simulation files to tinker more. |
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archimedes
Silver Member
United Kingdom
191 Posts |
Posted - 07/05/2009 : 23:39:12
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quote:
Originally posted by cctsim
I found it is far more effective to change C14. This graph is for C14= 10u, 1u, 0.47u and 0.1u. The green curve is the original. I can see now your complaints about too much bass.
Just to say I changed C14 to 1u and it did the trick regarding the excessive bass, thanks so much.
Your advice regarding C13 is also very useful, I changed this for 0.1u and took off some of the high end I didn't need.
Thanks
David |
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archimedes
Silver Member
United Kingdom
191 Posts |
Posted - 09/22/2009 : 23:08:02
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A quick update on this topic
Although C14 does indeed roll off the bass I still found that my OD-3 was 'barking' at me a little unpleasantly, particularly with chords lower on the fretboard. I began to think that this was because too much bass was hitting the clipping diodes d10 and d11. Although the R51 - C33 combination sets the frequency boosted at that point at about 720hz which (according to various items on the net) seems normal for an overdrive I think there is a fair bit of bass boost before these components. With this in mind I tried lowering the value of R51 to increase this frequency a bit. Using what I had to hand, a 390 ohm resistor, took it up to about 870z making the drive smoother and stopping the 'barking'. I have now put in a 500 ohm trimpot which has allowed me to tune this for the optimium point between meat and smoothness. Maybe this will be of use to someone. Just need that new level pot from Roland UK now.
David |
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cctsim
Silver Member
United Kingdom
418 Posts |
Posted - 09/23/2009 : 21:37:33
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I recently got to experiment with an OD-3. My problem is that there is not enough gain available as a stand alone pedal on the clean channel of a tube amp. My current mods initially were:
To reduce bass:
C14 to 1uF
To increase gain:
C33 to 1uF
R51 to 220 Ohm
With these two changes the cut-off is ~ 723 Hz
To remove the dip around 440 Hz in frequency before the gain stage.
C31 to 1 nF
Asymmetric clipping to add even harmonics:
C11 replaced with two 2N4148 diodes and a 100pF capacitor in parallel.
And the "crazy" bit:
I've removed C30 and inserted a Zvex Super-Hard-On booster that I built on a small board in its place. The booster has a trim potentiometer that I adjusted so that there is enough gain for my taste.
I could post some pictures if any there is interest.
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OD-3 trimpot to control bass?
